1. Field of the Invention
The present invention generally relates to a clamping apparatus for clamping a mold for injection molding (hereafter sometimes simply "mold"), and particularly, it relates to a clamping apparatus for a precise injection molding, which has a stationary part of a mold (hereafter "stationary mold") held by a stationary platen and a movable part of the mold (hereafter "movable mold") held by a movable platen and which performs a clamping between the stationary mold and the movable mold (hereafter sometimes "clamping of a mold" or simply "clamping"), as they are closely fitted to each other.
Further, the invention relates to a clamping apparatus for a precise injection molding that includes a stationary platen for holding a stationary mold, a cylinder actuator for moving a movable mold relative to the stationary mold to effect a clamping therebetween (hereafter simply "clamp cylinder"), a cylinder member of the clamp cylinder and/or one or more members integral therewith (hereafter collectively "cylinder body"), and a plurality of tie-rods interconnecting the stationary platen and the cylinder body, bearing reaction forces of the clamping.
2. Description of Relevant Art
FIG. 1 is a front view of a conventional clamping apparatus. As shown in FIG. 1, the conventional clamping apparatus includes a longitudinally extending frame 1 as a base thereof, a stationary platen 5 longitudinally slidably mounted thereon for holding a stationary mold 3, and a movable platen 7 longitudinally movable relative to the stationary platen 5. The movable platen 7 has a movable mold 11 held on a side thereof opposing the stationary platen 5, which movable mold 11 has a right face 11a in the figure cooperative with a left face 3a of the stationary mold 3 to define a space therebetween as a cavity for a molding.
The movable platen 7 is fixedly attached to an end portion 17a of a clamp ram 17 constituting an actuating part of a clamp cylinder 15, which is supported by a cylinder support 13 fixed to the frame 1.
As the clamp cylinder 15 is operated, the clamp ram 17 has an increasing or decreasing projection length, moving the movable platen 7 to advance close to or retreat away from the stationary platen 5. Between the stationary platen 5 and the cylinder support 13, there are provided a plurality of tie-rods 19 for a secure interconnection, which tie-rods 19 serve for longitudinally guiding the movable platen 7 in advance and retreat movements. At a righthand of the stationary platen 5, there is facing an injection nozzle 21 for injecting molten resin into the cavity to be defined between the stationary and movable molds 3, 11 after their clamping.
In the conventional clamping apparatus, as the clamp ram 17 is forced to extend by the clamp cylinder 15, the movable platen 7 advances as shown in FIG. 2, bringing the movable mold 11 into a close fitting with the stationary mold 13, where the mold is clamped, which clamping is performed with forces overcoming pressures of the molten resin injected inside the cavity, accompanying reaction forces pushing the stationary platen 5 rightwardly in the figure, with which forces the tie-rods 19 bear, deforming with an elongation, causing the stationary platen 5 and the cylinder support 13 to yield with their deformations, which deformations restrict each other.
In this respect, in the conventional apparatus, the cylinder support 13 stands as a cantilever member fixed at a lower end to the frame 1, with a tendency to have a yielding deformation of such a configuration 13a as illustrated by double-dash chain lines in FIG. 2, causing the stationary platen 5 to additionally deform in a rightwardly tilting manner. Accordingly, the stationary platen 5 has an increased sliding resistance to the frame 1 so that its sliding is additionally restricted in the clamping, with an increased tilting tendency, thus deforming with a vertically asymmetrical configuration 5a, resulting in a vertically asymmetrical distribution of deviations in terms of a parallelism between the stationary platen 5 and the movable platen 7.
Further, upper ones 19-1 of the tie-rods 19 are deformed in a different manner to lower ones 19-2, causing the movable platen 7 guided for movement by the respective tie-rods 19-1 and 19-2 to deform with deviations in parallelism to the stationary platen 5, with an increased vertical asymmetry.
Such deviations in parallelism between the platens 5, 7 adversely affects a clamping accuracy of the molds 3, 11, resulting in a non-conforming article, particularly in a precise injection molding needing a high accuracy, such as for production of an optical disc, e.g., a compact disc or a digital video disc.
FIG. 3 is a view along an arrow X of FIG. 1, as the stationary platen 5 is seen from an injection side. The stationary platen 5 is configured with a four-sided substantially rectangular shape, having at four corners thereof upper and lower pairs of left and right tie-rods 19-1a, 19-1b and 19-2a, 19-2b screwed to be securely fastened thereto by four nuts 9, respectively. All the nuts 9 have a righthanded screw tightening direction Y, i.e. clockwise in the figure.
Accordingly, when the nuts 9 are tightened, the respective corners of the stationary platen 5 have clockwise moments Z1, Z2, Z3, Z4 exerted thereon, so that an entirety of the platen 5 always has a superimposed clockwise moment Z acting thereon, needing time-consuming work for establishment and maintenance of its parallelism, whose negligence will adversely affect a clamping accuracy of mold, thus resulting in a non-conforming article, particularly in a precise injection molding, as described.